1. Field of the Invention
This invention relates to a semiconductor device, a display device, a producing method thereof, or a method using the semiconductor device or the display device. In specific, this invention relates to a semiconductor device and a display device each including a light-transmitting semiconductor layer, a producing method thereof, or a method using the semiconductor device or the display device. Further in specific, this invention relates to a liquid crystal display device including a light-transmitting semiconductor layer, a manufacturing method thereof, or a method the liquid crystal display device.
2. Description of the Related Art
In recent years, flat panel displays such as liquid crystal displays (LCDs) are becoming widespread. In specific, active-matrix LCDs provided with a transistor in each pixel are often used. As the transistor, the one which employs amorphous (non-crystalline) silicon or poly (polycrystalline) silicon for a semiconductor layer is widely used.
However, instead of the transistors formed using such silicon materials, transistors including light-transmitting semiconductor layers are considered. Further, a technique which increases an aperture ratio by employing light-transmitting electrodes as gate electrodes and source and drain electrodes is considered (see Reference 1 and Reference 2).    Reference 1: Japanese Published Patent Application No. 2007-123700    Reference 2: Japanese Published Patent Application No. 2007-81362
In general, a wiring for connecting elements such as transistors to each other is formed by extending conductive layers for forming a gate electrode and source and drain electrodes, whereby the wiring is formed in the same island as the conductive layers. Accordingly, a wiring for connecting gate of a transistor to gate of another transistor (such a wiring is called a gate wiring) is formed using the same layer structure and material as a gate electrode of the transistor; and a wiring for connecting source of the transistor to source of another transistor (such a wiring is called a source wiring) is formed using the same layer structure and material as a source electrode of the transistor, in many cases. Therefore, in the case where the gate electrode and the source and drain electrodes are formed using a light-transmitting material, the gate wiring and the source wiring are also formed using the light-transmitting material in many cases, like the gate electrode and the source and drain electrodes.
However, in general, as compared to a conductive material having light-shielding property and a reflecting property, such as aluminum (Al), molybdenum (Mo), titanium (Ti), tungsten (W), neodymium (Nd), Copper (Cu), or silver (Ag), a light-transmitting conductive material such as indium tin oxide (ITO), indium zinc oxide (IZO), or indium tin zinc oxide (ITZO) has low conductivity. Accordingly, if a wiring is formed using a light-transmitting conductive material, wiring resistance becomes high. For example, in the case where a large display device is manufactured, wiring resistance becomes very high because a wiring is long. As wiring resistance increases, the waveform of a signal which is transmitted through the wiring becomes distorted, resulting in a low voltage supply due to a voltage drop through the wiring resistance. Therefore, it is difficult to supply normal voltage and current, whereby normal display and operation become difficult.
On the other hand, in the case where a gate wiring and a source wiring are formed using a light-shielding conductive material by using the light-shielding conductive material for the gate electrode and the source and drain electrodes, distortion of the waveform of the signal can be suppressed due to an increase in the conductivity of the wiring. However, since a light-shielding material is used for the gate electrode and the source and drain electrodes, aperture ratio decreases and power consumption becomes high.
In addition, in terms of display performance, high storage capacitance and higher aperture ratio are demanded for pixels. Pixels each having high aperture ratio increase the use efficiency of light, so that power saving and miniaturization of a display device can be achieved. In recent years, the size of pixels has been miniaturized and images with higher definition are demanded. The miniaturization of the size of the pixel causes a decrease in the aperture ratio of the pixel because of large formation area for transistors and wirings which occupies one pixel. Accordingly, in order to obtain a high aperture ratio in each pixel in a regulation size, the circuit configuration of the pixel needs to have an efficient layout of necessary components.
In view of the foregoing problems, one object of an embodiment in this invention is to provide a semiconductor device with high aperture ratio and a manufacturing method thereof. In addition, one object of one embodiment in this invention is to provide a semiconductor device with low power consumption and a manufacturing method thereof.
In order to solve the above problem, one embodiment of this invention is a semiconductor device which includes a gate wiring including a gate electrode, in which a first conductive film and a second conductive film are stacked in this order, a gate insulating film covering the gate electrode and the gate wiring, an island-shaped semiconductor film provided over the gate electrode with the gate insulating film interposed therebetween, a source wiring including a source electrode, in which a third conductive film and a fourth conductive film are stacked in this order, an interlayer insulating film covering the island-shaped semiconductor film and the source wiring including the source electrode, a pixel electrode provided over the interlayer insulating film and electrically connected to the island-shaped semiconductor film, and a capacitor wiring. The gate electrode is formed of the first conductive film. The gate wiring is formed of the first conductive film and the second conductive film. The source electrode is formed of the third conductive film. The source wiring is formed of the third conductive film and the fourth conductive film.
Further, one embodiment in this invention is a semiconductor device which includes a plurality of gate wirings formed by being extended in a first direction, a plurality of source wirings extended in a second direction which intersects with the gate wirings, a plurality of pixel portions defined by the gate wiring and the source wiring, a gate electrode formed in each of the pixel portions and extended from the gate wiring, and a switching element including a source electrode extended from the source wiring. The gate wiring is formed of a first conductive film and a second conductive film thereover. The source wiring is formed of a third conductive film and a fourth conductive film thereover. The gate electrode is formed of the first conductive film. The source electrode is formed of the third conductive film.
Further, in one embodiment of this invention, the first conductive film and the third conductive film preferably have a light-transmitting property. Furthermore, in one embodiment of this invention, the second conductive film and the fourth conductive film preferably have a light-shielding property. Furthermore, in one embodiment of this invention, the second conductive film and the fourth conductive film have higher conductivity than the first conductive film and the third conductive film.
Further, in one embodiment of this invention, the second conductive film is formed of one or a plurality of elements selected from Al, Ti, Cu, Au, Ag, Mo, Ni, Ta, Zr, and Co. Furthermore, in one embodiment of this invention, the fourth conductive film is formed of one or a plurality of elements selected from Al, Ti. Cu, Au, Ag, Mo, Ni, Ta, Zr, and Co.
By employing such a structure, a light-transmitting transistor or a light-transmitting capacitor element can be formed. Therefore, even though the transistor or the capacitor element is provided in a pixel, a decrease in an aperture ratio can be suppressed. Further, since a wiring for connecting the transistor and an element (e.g., another transistor) or a wiring for connecting the capacitor element and an element (e.g., another capacitor element) is formed by using a material with low resistivity and high conductivity, the blunting of the waveform of a signal and a voltage drop due to wiring resistance can be suppressed.
Further, one embodiment of this invention is a semiconductor device in which the semiconductor film is any one of zinc oxide, titanium oxide, magnesium zinc oxide, cadmium zinc oxide, cadmium oxide, InGaO3(ZnO)5, and an In—Ga—Zn—O based amorphous oxide semiconductor.
Further, one embodiment of this invention is a manufacturing method of a semiconductor device, in which a first conductive film and a second conductive film are sequentially formed over a light-transmitting insulating substrate, a first resist mask having a portion where a stacked layer of the first conductive film and the second conductive film remain and a portion where only the first conductive film remains, whose thicknesses are different from each other is formed by photolithography with a multi-tone mask, the first conductive film and the second conductive film are etched by using the first resist mask, a second resist mask is formed by ashing the first resist mask, the second conductive film is etched by using the second resist mask and part of the first conductive film is exposed, a first insulating film is formed so as to cover the insulating substrate, the first conductive film, and the second conductive film, an island-shaped semiconductor film is formed over the first conductive film with the first insulating film interposed therebetween, a third conductive film and a fourth conductive film are sequentially formed over the insulating film, a third resist mask having a portion where a stacked layer of the third conductive film and the fourth conductive film remain and a portion where only the first conductive film remains, whose thicknesses are different from each other is formed by photolithography with a multi-tone mask, the third conductive film and the fourth conductive film are etched by using the third resist mask, a fourth resist mask is formed by ashing the third resist mask, and the fourth conductive film is formed by using the fourth resist mask and part of the third conductive film is exposed.
Further in the conductive layers, a light-transmitting region (a region with high light transmittance) and a light-shielding region (a region with low light transmittance) can be formed by one mask (reticle) with use of a multi-tone mask. Accordingly, the light-transmitting region (the region with high light transmittance) and the light-shielding region (the region with low light transmittance) can be formed without increasing the number of masks.
Note that semiconductor devices in this specification mean all devices which can function by utilizing semiconductor characteristics, and display devices, semiconductor circuits, and electronic devices are all semiconductor devices.
According to one embodiment of this invention, the light-transmitting transistor or the light-transmitting capacitor element can be formed. Therefore, even if the transistor or the capacitor is provided in a pixel, aperture ratio can be made high. Further, since a wiring for connecting the transistor and an element (e.g., another transistor) or a wiring for connecting a capacitor element and an element (e.g., another capacitor element) can be formed by using a material with low resistivity and high conductivity, the distortion of the waveform of a signal and a voltage drop due to wiring resistance can be reduced.